Composite adsorbent and process for producing same

ABSTRACT

A composite adsorbent comprising an acid salt of an m- or p-aromatic amino acid and an acid. The adsorbent may further contain a transition metal compound. The former removes aldehydes, ammonias and amines simultaneously, and the latter further removes hydrogen sulfide. 
     The composite adsorbent is used in the form of a powder, a solution, or a solid supported on a carrier.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a composite adsorbent which effectivelyremoves various offensive odors of amines, aldehydes, sulfides, etc.originating for industrial and automotive exhaust gas, and other smellsof tobacco, human body, human waste, foods, etc. encountered in dailylife.

2. Description of the Related Art

Human activities in living rooms, offices, kitchens, automobiles, etc.accompany various offensive odors. It is said that offensive odors in acar contain thousands of components originating from cigarette smoke,sweat, exhaust gas, dust, etc. The Offensive Odor Control Law (Japaneselaw) describes the following twelve components as important, namely,ammonia, methyl mercaptan, hydrogen sulfide, methyl sulfide, methyldisulfide, trimethylamine, acetaldehyde, styrene, n-butyric acid, n-,iso-valeric acid, and propionic acid.

The conventional methods of removing such offensive odors are by maskingwith an aromatic or by adsorption with activated carbon or silica gel.However, these methods have disadvantages. Masking with an aromatic doesnot remove the components of offensive odors in itself, and there may bean instance where the aromatic itself smells unpleasant. As to activatedcarbon and silica gel, they limit their adsorbate. For example,activated carbon is not effective at all for odors originating from suchbasic substances as ammonia and trimethylamine.

Another method is chemical removing. It removes offensive odors by thechemical reaction like an acid-base neutralization reaction. It permitsthe sure removal of both acid odors of acetaldehyde, hydrogen sulfide,etc. and basic odors of ammonia, trimethylamine, etc. More precisely,acid odors and basic odors are removed by neutralization with a basicadsorbent and an acid adsorbent, respectively. However, this chemicaladsorbent has also a disadvantage that the basic adsorbent and the acidadsorbent react with each other and become deactivated when they aresupported on the same carrier or dispersed in the same liquidsimultaneously. This makes it necessary to use separate carriers for thebasic and acid adsorbents. As the result, the net amount of eachingredient that can be supported on carriers is reduced and hence theresulting composite adsorbent decreases in deodorizing capacity.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new compositeadsorbent which effectively and simultaneously adsorbs acid gases suchas lower aldehyde and basic gases such as ammonia.

It is another object of the present invention to provide a new compositeadsorbent which is composed of two chemically different adsorbents (onebeing a reductant such as amino acid and the other being an oxidant suchas transition metal salt) supported together on the same carrier. Thecomposite adsorbent is as effective in deodorizing performance as asingle adsorbent in itself, because coexistence of different adsorbentsprevents any decrease in effectiveness caused by separate supporting.

The present inventors carried out a series of researches to eliminatethe disadvantages involved in the related art technology and to developa new composite adsorbent which can effectively and simultaneouslyremove an offensive odor composed of many smelling components, and theycompleted the present invention which is embodied in a compositeadsorbent.

According to the first aspect of the present invention, the compositeadsorbent comprises at least one acid salt selected from the groupconsisting of acid salts of a m-aromatic amino acid and a p-aromaticamino acid, and at least one acid. It is noticeable that an acid salt ofm- or p-a romatic amino acid effectively removes an offensive odor oflower aldehyde (which is acidic ) although it is an acid substance. Thisis, presumably, because lower aldehydes are adsorbed and deactivated bythe cooperative and synergistic chemical reaction of the acidified aminogroup forming an acid salt with the carboxylic group in the amino acid.The acid coexisting with an acid salt of an amino acid functions toremove basic gases such as ammonia and trimethylamine through thewell-known acid-base reaction.

The composite adsorbent of the present invention is highly effective inremoving offensive odors originating from acid gases such as loweraldehydes and offensive odors originating from basic gases such asammonia and trimethylamine. Therefore, it is very useful for theoffensive odors containing many smelling components which are present inthe living environment such as automobiles, kitchens, living rooms, andoffices.

According to the second aspect of the present invention, the compositeadsorbent comprises at least one acid salt selected from the groupconsisting of acid salts of a m-aromatic amino acid and a p-aromaticamino acid, at least one acid, and at least one transition metalcompound. The additional transition metal compound effectively removesoffensive odors originating from sulfides such as hydrogen sulfide andmethyl mercaptan. This effect stems from the ability of the transitionmetal compound to react with sulfide gases to form metal sulfides.

Usually, a transition metal compound cannot coexist stably with anaromatic amino acid because of the acid-base reaction that takes placebetween the amino group in the amino acid and the transition metalcompound. However, this is not true of an aromatic amino acid in theform of acid salt.

In this case, the amino group forming a salt with the acid added in anexcess amount does not react with the transition metal compound. Inother words, the second aspect of the present invention was realized bythe addition of an excess acid which permits not only the removal ofoffensive odors originating from basic gases but also the coexistence ofan aromatic amino acid with a transition metal compound.

According to the second aspect of the present invention, the threeactive ingredients can be uniformly supported together and highlydispersed on a porous carrier because they are not reactive with oneanother. Therefore, the composite adsorbent is highly effective inremoving offensive odors originating from many gases of different naturesuch as ammonia, hydrogen sulfide, and acetaldehyde. It is very usefulfor the offensive odors containing many smelling components which arepresent in the living environment such as automobiles, kitchens, livingrooms, and offices.

These and other objects of the present invention will become moreapparent in the detailed description and examples which follow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the first aspect of the present invention, the compositeadsorbent comprises at least one acid salt selected from the groupconsisting of acid salts of a m-aromatic amino acid and a p-aromaticamino acid, and at least one acid. The former component is prepared bymixing said acid with said amino acid or a salt of said amino acid. Theacid donates a proton to the amino group of the m- or p-aromatic aminoacid, thereby changing the aromatic amino acid into an acid salt. If theacid is added in an excess amount, the resulting product is a mixture ofan acid salt of m- or p-aromatic amino acid and an acid. As the aromaticamino acid, an aromatic monoamino-monocarboxylic acid can be employed,and especially a m- or p-aminobenzoic acid or p-aminosalicylic acid arepreferable.

The acid includes inorganic acids (such as hydrochloric acid, nitricacid, sulfuric acid, phosphoric acid, and pyrophosphoric acid) andorganic acids (such as citric acid, malonic acid, malic acid, and oxalicacid). If the composite adsorbent is intended for use at hightemperatures, the acid should preferably be a non-volatile one such assulfuric acid, phosphoric acid, and oxalic acid.

According to the second aspect of the present invention, the compositeadsorbent comprises at least one acid salt selected from the groupconsisting of acid salts of a m-aromatic amino acid and p-aromatic aminoacid, at least one acid, and at least one transition metal compound.Examples of the third component include nitrate, sulfate, carbonate,phosphate, pyrophosphate, chloride, bromide, and fluoride of arsenic,mercury, copper, antimony, bismuth, tin, cadmium, lead, zinc, cobalt,nickel, iron, and manganese, the most desirable of which are chloride,bromide, and fluoride of copper, zinc, cobalt, and nickel.

There are no restrictions on the usage of the composite adsorbentspertaining to the first and second aspects of the present invention.They may be used as such in powder form. For a better effect, they maybe used in the form of solution in an adequate concentration or in theform of solid supported on a porous carrier. Examples of the porouscarrier include inorganic porous carriers (such as sepiolite,palygorskite, activated carbon, zeolite, activated carbon fiber,activated alumina, sepiolite-mixed paper, silica gel, activated clay,vermiculite, and diatomaceous earth), and organic porous carriers (suchas pulp, fibers, cloth, and polymeric cellular body), the most desirableof which are sepiolite, palygorskite, activated carbon, activatedalumina, and zeolite.

The porous carrier supports the active ingredients of the compositeadsorbent in its pores uniformly, so that the active ingredients have anenlarged area that comes into contact with the gases of offensive odorand hence adsorb them efficiently. In addition, the porous carrieritself has the capability for adsorption and hence enhances theperformance of the composite adsorbent. For example, activated carbonand sepiolite are effective respectively in adsorption of offensiveodors originating from hydrocarbon gases and lower fatty acids. Theporous carrier may be in the form of sheet, honeycomb, powder, pellet,granule, plate, fiber, etc.

There are no restrictions on the method by which the composite adsorbentis supported on the above-mentioned porous carrier. Supporting may beaccomplished by mixing the composite adsorbent with the porous carrier,both in the form of fine particles. Alternatively, supporting shouldpreferably be accomplished by impregnating the porous carrier with asolution of the composite adsorbent in water (or any other adequatesolvent ). The latter method is effective in the uniform dispersion ofthe active ingredients on the porous carrier, which leads to the maximumdeodorizing performance.

According to the present invention, it is desirable that the activeingredients of the composite adsorbent should be supported in an amountof 0.1-30 wt% of the porous carrier. With an amount less than 0.1 wt%,the active ingredients of the composite adsorbent are not enough toproduce a good deodorizing effect. With an amount in excess of 30 wt%,the active ingredients of the composite adsorbent are not uniformlydispersed on the porous carrier, with the result that the compositeadsorbent does not fully exhibit its deodorizing performance and theporous carrier itself decreases in the gas adsorbing capacity. Apreferred amount ranges from 0.5 to 15 wt%.

It is necessary that the ratio of the active ingredients and the kind ofthe porous carrier should be properly selected according to the majorconstituent gases of the offensive odor to be removed.

Having generally described this invention, a further understanding canbe obtained by reference to specific examples which are provided hereinfor purposes of illustration only and are not intended to be limitingunless otherwise specified.

EXAMPLE 1

An aqueous solution containing an acid salt of an aromatic amino acidand an acid was prepared by dissolving an aromatic amino acid and anacid according to the formulation for Sample No. 1 as shown in Table 1.In the preparation of the aqueous solution, the acid was added in anexcess amount so that the amino group in the aromatic amino acid issupplied with a proton for the formation of ammonium ion.

                                      TABLE 1                                     __________________________________________________________________________    Composition of Composite Adsorbent                                                                    Transition metal                                      Sample No.                                                                          Amino acid (g)                                                                         Acid (g) Compound (g)                                                                           Water (g)                                    __________________________________________________________________________    1     p-aminobenzoic                                                                         85% phosphoric                                                                         --       200                                                acid (12)                                                                              acid (18)                                                      2     p-aminobenzoic                                                                         85% phosphoric                                                                         Cupric chloride                                                                        200                                                acid (12)                                                                              acid (18)                                                                              dihydrate (12)                                        3     p-aminobenzoic                                                                         96% sulfuric                                                                           Cupric chloride                                                                        200                                                acid (12)                                                                              acid (20.2)                                                                            dihydrate (12)                                        4     m-aminobenzoic                                                                         36% hydrochloric                                                                       Cupric chloride                                                                        200                                                acid (12)                                                                              acid (17.8)                                                                            dihydrate (12)                                        5     p-aminosalicylic                                                                       Oxalic acid (14.1)                                                                     Cupric chloride                                                                        200                                                acid (12)         dihydrate (12)                                        6     p-aminobenzoic                                                                         85% phosphoric                                                                         Nickel chloride                                                                        200                                                acid (12)                                                                              acid (18)                                                                              hexahydrate (12)                                      C-1   --       --       Cupric chloride                                                                        200                                                                  dihydrate (12)                                        C-2   o-aminobenzoic                                                                         --       --       200                                                acid (12)                                                               __________________________________________________________________________

The aqueous solution was impregnated into 300 g of activated carbon (4-6mesh) obtained from coconut shell. After drying at 100° C. for 10 hours,there was obtained a composite adsorbent (sample No. 1).

The thus obtained composite adsorbent was tested for adsorptivity foracetaldehyde, ammonia, and hydrogen sulfide in the following manner. Onegram of the composite adsorbent was placed in a 5-liter impermeable bag.Into this bag were introduced 425 ppm of acetaldehyde, 900 ppm ofammonia, and 10000 ppm of hydrogen sulfide. The bag was left sealed atroom temperature for 24 hours. The concentration of the gases remainingin the bag was measured, and it was translated into the removal ratio (%) according to the formula below. ##EQU1## where

A: blank concentration

B: residual concentration

("Blank concentration" denotes the concentrations of the gases remainingin the bag containing no adsorbent after a prescribed period of time.The blank concentrations of acetaldehyde, ammonia, and hydrogen sulfideare 401.1 ppm, 820 ppm, and 7200 ppm, respectively.)

The determination of acetaldehyde was by gas chromatography under theconditions shown in Table 2, and the determination of ammonia andhydrogen sulfide was by a gas detecting tube. The results of thedeterminations are shown in Table 3 (Sample No. 1).

For comparison, the same experiment as mentioned above was carried outusing cupric chloride alone or o-aminobenzoic acid alone supported onthe carrier. The results are shown in Table 3 (Sample Nos. C-1 and C-2).

It is noted from Table 3 that the composite adsorbent in Example 1 is byfar superior in adsorptivity of both acetaldehyde and ammonia to thecomparative samples.

                  TABLE 2                                                         ______________________________________                                        Column     FAL-M 10%, Shimalite TPA glass, 3 m ×                                   3 mm dia.                                                          Column     75° C.                                                      temperature                                                                   Carrier gas                                                                              Nitrogen, 30 ml/min                                                Detector   FID                                                                Apparatus  GC-15A, Shimdadzu Seisakusho Ltd.                                  ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Smelling    Sample  Residual con- Removal                                     gas         No.     centration (ppm)                                                                            ratio (%)                                   ______________________________________                                        Acetaldehyde                                                                              1       2.0           99                                                      2       2.1           99                                                      3       not detected  100                                                     4       24.8          93                                                      5       40.0          90                                                      6       not detected  100                                                     C-1     320.6         20                                                      C-2     63.6          84                                          Ammonia     1       7.3           99                                                      2       7.5           99                                                      3       0.4           99                                                      4       2.7           99                                                      5       98.0          88                                                      6       20.0          97                                                      C-1     85.9          89                                                      C-2     666.2         18                                          Hydrogen sulfide                                                                          1       5215.7        27                                                      2       750.0         85                                                      3       2.0           99                                                      4       not detected  100                                                     5       1.7           99                                                      6       5200.0        27                                                      C-1     not detected  100                                                     C-2     260.0         96                                          ______________________________________                                    

EXAMPLE 2

Aqueous solutions each containing an acid salt of an aromatic aminoacid, an acid, and a transition metal compound were prepared bydissolving an aromatic amino acid, an acid, and a transition metalcompound according to the formulation for Sample Nos. 2-6 as shown inTable 1. In the preparation of the aqueous solutions, the acid was addedin an excess amount so that the amino group in the aromatic amino acidis supplied with a proton for the formation of ammonium ion.

Each of the aqueous solutions was impregnated into 300 g of activatedcarbon (4-6 mesh) obtained from coconut shell. After drying at 100° C.for 10 hours, there were obtained composite adsorbents (sample Nos.2-6).

The thus obtained composite adsorbents were tested for adsorptivity foracetaldehyde, ammonia, and hydrogen sulfide in the same manner as inExample 1. The results are shown in Table 3 (Sample Nos. 2-6). It isnoted from Table 3 that the composite adsorbents in Example 2 are by farsuperior in adsorptivity of all of acetaldehyde, ammonia and hydrogensulfide to the comparative samples.

What is claimed is:
 1. A composite adsorbent for removing offensive odors from a gas comprising as active ingredients at least one acid salt selected from the group consisting of acid salts of a m-aromatic amino acid and a p-aromatic amino acid, and at least one acid and at least one transition metal compound.
 2. A composite adsorbent as claimed in claim 1, wherein the aromatic amino acid is an aromatic monoamino-monocarboxylic acid.
 3. A composite adsorbent as claimed in claim 2, wherein the aromatic monoamino-monocarboxylic acid is one selected from the group consisting of a m-aminobenzoic acid, a p-aminobenzoic acid and a p-aminosalicylic acid.
 4. A composite adsorbent as claimed in claim 1, wherein the acid is an inorganic acid.
 5. A composite adsorbent as claimed in claim 4, wherein the inorganic acid is a member selected from the group consisting of a hydrochloric acid, a nitric acid, a sulfuric acid, a phosphoric acid, and a pyrophosphoric acid.
 6. A composite adsorbent as claimed in claim 1, wherein the acid is an organic acid.
 7. A composite adsorbent as claimed in claim 6, wherein the organic acid is a member selected from the group consisting of a citric acid, a malonic acid, a malic acid, and an oxalic acid.
 8. A composite adsorbent as claimed in claim 1, wherein the transition metal compound is a member selected from the group consisting of salts of arsenic, mercury, copper, antimony, bismuth, tin, cadmium, lead, zinc, cobalt, nickel, iron and manganese.
 9. A composite adsorbent as claimed in claim 1, wherein the transition metal compound is a member selected from the group consisting of a nitrate, a sulfate, a carbonate, a phosphate, a pyrophosphate, a chloride, a bromide, and a fluoride.
 10. A composite adsorbent as claimed in claim 1, wherein the active ingredients are supported uniformly on a porous carrier.
 11. A composite adsorbent as claimed in claim 10, wherein the porous carrier is a member selected from the group consisting of inorganic porous carriers of sepiolite, palygorskite, activated carbon, zeolite, activated carbon fiber, activated alumina, sepiolite-mixed paper, silica gel, activated clay, vermiculite, and diatomaceous earth, and organic porous carriers of pulp, fibers, cloth, and a polymeric cellular body.
 12. A composite adsorbent as claimed in claim 10, wherein the active ingredients are supported on the porous carrier in the amount of 0.1-30 wt% of the porous carrier.
 13. A composite adsorbent as claimed in claim 1, wherein the active ingredients are supported uniformly on a porous carrier.
 14. A composite adsorbent as claimed in claim 13, wherein the active ingredients are supported on the porous carrier in the amount of 0.1-30 wt% of the porous carrier. 